Organic dye for a dye-sensitized solar cell

ABSTRACT

Organic dye for a dye-sensitized solar cell (DSSC) comprising at least one electron-acceptor unit and at least one π-conjugated unit. Said organic dye is particularly useful in a dye-sensitized photoelectric transformation element which, in its turn, can be used in a dye-sensitized solar cell (DSSC).

The present invention relates to an organic dye for a dye-sensitized solar cell (DSSC).

More in particular, the present invention relates to an organic dye for a dye-sensitized solar cell (DSSC) comprising at least one electron-acceptor unit and at least one π-conjugated unit.

Said organic dye is particularly useful in a dye-sensitized photoelectric transformation element which, in its turn, can be used in a dye-sensitized solar cell (DSSC).

Consequently, it is a further object of the present invention a dye-sensitized photoelectric transformation element comprising the organic dye above reported, as well as a dye-sensitized solar cell (DSSC) comprising said photoelectric transformation element.

Dye-sensitized solar cells (DSSCs) have been developed by Gratzel et al. on 1991 and they have attracted considerable attention in recent years due to their high efficiency and remarkably low manufacture cost compared to the existing silicon solar cells.

The dye-sensitized solar cells (DSSCs) are photoelectrochemical solar cells mainly comprising organic dye molecules capable of absorbing visible light to generate electron-hole pair, and transition metal oxide for transmitting the generated electrons.

As organic dyes for dye-sensitized solar cells (DSSCs), ruthenium metal complexes which show high photoelectric transformation efficiency has been widely used. However, ruthenium metal complexes contain expensive ruthenium metal and usually require careful synthesis and tricky purification steps.

Recently, it has been found that metal-free organic dyes which show excellent properties in terms of absorption efficiency, oxidation reduction stability and intramolecular charge-transfer (CT) absorption, may be used for dye-sensitized solar cells (DSSCs) as an alternative of expensive ruthenium metal complexes.

Metal-free organic dyes, generally, comprise electron donor unit-electron acceptor unit connected by π-conjugated unit. For most metal-free organic dyes, arylamine derivatives function as electron-donor unit and cyanoacrylic acid or rodhanine residue functions as electron acceptor unit, and they are connected by π-conjugated unit such as, for example, methanine unit or thiophene chain.

A lot of studies have been carried out with regard to said metal-free organic dyes.

For example, Tan S. et al. in the article “Novel Carboxylated Oligothiophenes as Sensitizers in Photoelectric Conversion Systems”, Chemistry—A European Journal (2005), Vol. 11, Issue 21, pg. 6272-6276, disclose novel carboxylated oligothiophenes with different thiophene units as photosensitisers in dye-sensitized solar cells (DSSCs). It is said that the introduction of —COOH group into thiophene molecules may led to a red shift of UV-visible absorption, increase light-harvesting efficiency and enhance photoinduced charge transport by forming efficient covalent bonds to the substrate surface. It is also said that the dye-sensitized solar cells (DSSCs) based on said oligothiophenes have excellent performances: in particular, under irradiation of 100 mW·cm⁻² a short-circuit current of 10.57 mA·cm⁻² and an overall photoelectric transformation efficiency (q) of 3.36% is achieved, when pentathiophene dicarboxylated acid was used as a sensitizer.

Tanaka K. et al. in the article “Development and Photovoltaic Performance of Oligothiophene-sensitized TiO₂ Solar Cells”, Chemistry Letters (2006), Vol. 35, No. 6, pg. 592-593, disclose novel dye-sensitized TiO₂ solar cells using a variety of oligothiophenecarboxylic acids. It is said that said solar cells show relatively high photovoltaic performances, i.e a photoelectric transformation efficiency (η) ranging from 0.41% to 1.29%, which are largely dependent on the chain lengths of the oligothiophenes and on the number of the carboxylic groups.

Mishra A. et al. in the review “Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules”, Angewandte Chemie (2009), Vol. 48, pg. 2474-2499, disclose recent advances in molecular design and technological aspects of metal-free organic dyes for application in dye-sensitized solar cells (DSSCs). Special attention has been paid to the design principles of this organic dyes and on the effect of various electrolyte systems. Co-sensitization, an emerging technique to extend the absorption range, is also discussed as a way to improve the performance of the device. In addition, inverted organic dyes for photocatode are also described, which constitute a relatively new approach for the production of tandem cells. Moreover, special consideration has been paid to the correlation between the molecular structure and the physical properties of the metal-free organic dyes with regard to their performances in dye-sensitized solar cells (DSSCs).

Yang H. et al. in the article “Organic Dyes Incorporating the Dithieno[3,2-b:2′,3′-d]thiophene Moiety for Efficient Dye-Sensitized Solar Cells”, Organic Letters (2010), Vol. 12, No. 1, pg. 16-19, disclose new dipolar compounds incorporating dithieno[3,2-b:2′,3′-d]thiophene unit as the electron-donor, an oligothiophene as the conjugated spacer and 2-cyanoacrylic acid as the electron acceptor. These non-arylamine type metal-free organic compounds are said to be successfully used as the sensitizers of dye-sensitized solar cells (DSSCs): in particular, under AM 1.5 G irradiation the photoelectric transformation efficiency (η) ranges from of 3.54% to 5.15%.

Sahu D. et al. in the article “Synthesis and applications of novel acceptor-donor-acceptor organic dyes with dithienopyrrole- and fluorene-cores for dye-sensitized solar cells”, Tetrahedron (2011), Vol. 67, No. 2, pg. 303-311, disclose new symmetrical organic dyes including a fluorene or a dithienopyrrole unit as electron donor, an oligothiophene as the conjugated spacer and two 2-cyanoacrylic acid groups as the electron acceptor. It is said that the dye-sensitized solar cells (DSSCs) comprising said organic dyes, in particular in the case of dyes including a fluorene unit, have a photoelectric transformation efficiency (q) of 4.73% under irradiation of 100 mW·cm⁻² and a maximum incident photon conversion efficiency (IPCE) of about 76% under AM 1.5 simulated solar irradiance.

Warnan J. et al. in the article “Application of Poly(3-hexylthiophene) Functionalized with an Anchoring Group in Dye-sensitized Solar Cells”, Macromolecular Rapid Communication (2011), Vol. 32, DOI: 10.1002/marc.201100214, disclose a series of three poly(3-hexylthiophene) functionalized either with a cyanoacetic acid (CA) or a rhodanine-3-acetic acid anchoring groups, which were synthesized and characterized. The titanium dioxide (TiO₂) based dye-sensitized solar cells (DSSCs) have been fabricated and performances were tested. It is said that the dye-sensitized solar cells (DSSCs) comprising said poly(3-hexylthiophene) show a photoelectric transformation efficiency (η) of 3.02% under irradiation of 100 mW·cm⁻² and a maximum incident photon conversion efficiency (IPCE) of about 50% under AM 1.5 simulated solar irradiance.

However, most of the organic dyes already known may exhibit low photoelectric transformation efficiency (η) compared to ruthenium metal complex dyes. Therefore, there have been continuous attempts to develop novel organic dyes able to give dye-sensitized solar cells (DSSCs) having improved photoelectric transformation efficiency (η) compared to the existing organic dyes.

The Applicant has faced the problem of finding an organic dye able to give dye-sensitized solar cells (DSSCs) having improved photoelectric transformation efficiency (η), i.e. a photoelectric transformation efficiency (η) higher than or equal to 7.5%.

The Applicant has found an organic dye comprising at least one electron-acceptor group and at least one π-conjugated unit which is able to give a dye-sensitized solar cell (DSSC) having improved photoelectric transformation efficiency (η), i.e. a photoelectric transformation efficiency (η) higher than or equal to 7.5%. Moreover, said dye-sensitized solar cells (DSSCs) also have improved Voc (open circuit photovoltage), FF (fill factor) and Jsc (short-circuit photocurrent density).

An object of the present invention therefore relates to an organic dye having general formula (I):

wherein:

-   -   X and Z, equal to or different from each other, represent a         hydrogen atom; or are selected from: —COOH group, phosphonic         groups having formula —PO(OH)₂ or —PO(OH)(R) wherein R         represents a C₁-C₂₀, preferably C₂-C₈, alkyl group, linear or         branched, C₁-C₂₀, preferably C₄-C₁₂, alkyl groups, linear or         branched, saturated or unsaturated, optionally containing         heteroatoms, C₄-C₁₂, preferably C₅-C₈, cicloalkyl groups         optionally substituted, carboxycyanovinylene groups having         general formulae (II), (III), (IV), (V), (VI), (VII), (VIII),         (IX), (X):

-   -   wherein R₅, R₆ and R₇, equal to or different from each other,         represent an hydrogen atom, or are selected from C₁-C₂₀,         preferably C₂-C₈, alkyl groups linear or branched; W represents         an oxygen atom or a sulphur atom; with the proviso that at least         one of X and Z is not an hydrogen atom, an alkyl group, or a         cycloalkyl group;     -   R₁ and R₂, equal to or different from each other, are selected         from: C₁-C₂₀, preferably C₄-C₁₂, alkyl groups, linear or         branched, saturated or unsaturated, optionally containing         heteroatoms, C₄-C₁₂, preferably C₅-C₈, cycloalkyl groups,         optionally substituted, C₄-C₁₁, preferably C₅-C₇, heterocyclic         groups, optionally substituted, trialkyl- or triaryl-silyl         groups;     -   R₃ and R₄, equal to or different from each other, represent a         hydrogen atom; or are selected from: C₁-C₂₀, preferably C₄-C₁₂,         alkyl groups, linear or branched, saturated or unsaturated,         optionally containing heteroatoms, C₄-C₁₂, preferably C₄-C₈,         cycloalkyl groups optionally substituted, C₆-C₂₄, preferably         C₆-C₁₄, aryl groups optionally substituted, heteroaryl groups         optionally substituted, C₄-C₁₁, preferably C₅-C₇, heterocyclic         groups optionally substituted, alkoxyl or aryloxyl groups         optionally substituted, thioalkoxyl or thioaryloxyl groups         optionally substituted, trialkyl- or triaryl-silyl groups,         halogen atoms such as, for example, fluorine, chlorine, bromine,         iodine, preferably fluorine;     -   or, R₃ and R₄ can be optionally bound to each other to form,         together with the other atoms to which they are bound, a         saturated, unsaturated or aromatic, cycle containing from 1 to         12 carbon atoms, optionally substituted with C₁-C₂₀, preferably         C₂-C₈, alkyl groups, linear or branched, saturated or         unsaturated, optionally containing heteroatoms, C₆-C₂₄,         preferably C₆-C₁₄, aryl groups optionally substituted,         heteroaryl groups optionally substituted, C₄-C₁₂, preferably         C₄-C₈, cycloalkyl groups optionally substituted, C₄-C₁₁,         preferably C₅-C₇, heterocyclic groups optionally substituted,         trialkyl- or triaryl-silyl groups, alkoxyl or aryloxyl groups         optionally substituted, thioalkoxyl or thioaryloxyl groups         optionally substituted, halogen atoms such as, for example,         fluorine, chlorine, bromine, iodine, preferably fluorine, cyano         groups, nitro groups; said cycle optionally containing other         heteroatoms such as, for example, oxygen, sulphur, nitrogen,         silicon, phosphorous, selenium, boron;     -   n and p are integer numbers ranging from 0 to 3, preferably from         0 to 2;     -   m is an integer number ranging from 0 to 5, preferably from 0 to         2;     -   with the proviso that at least one of n and p is different from         0.

For the aim of the present description and of the following claims, the definitions of the numerical ranges always comprise the extremes unless otherwise specified.

For the aim of the present description and of the following claims, the term “comprising” also includes the terms “which essentially consists of” or “which consists of”.

In accordance with a preferred embodiment of the present invention, in said general formula (I):

-   -   X is a hydrogen atom, or a carboxycyanovinylene group having         general formula (II):

-   -   wherein R₅ is an hydrogen atom;     -   Z is a carboxycyanovinylene group having formula (II) or (IV):

-   -   wherein R₅ is an hydrogen atom;     -   R₁ and R₂, equal to each others, are a n-hexyl group, a n-octyl         group, a n-decyl group, a n-dodecyl group, preferably a n-octyl         group;     -   R₃ and R₄, equal to or different from each other, are a hydrogen         atom or a n-hexyl group, a n-octyl group, a n-decyl group, a         n-dodecyl group, preferably a hydrogen atom or a n-octyl group;         or, R₃ and R₄ are bound to each other to form, together with the         other atoms to which they are bound, a saturated cycle         containing 4 carbon atoms and two oxygen atoms, preferably, they         form a 1,4-dioxane;     -   n is 1, m is 1, p is 0 or 1.

The term “C₁-C₂₀ alkyl groups” means linear or branched alkyl groups having from 1 to 20 carbon atoms, saturated or unsaturated. Specific examples of C₁-C₂₀ alkyl groups are: methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, 2-ethylheptyl, 2-ethylhexyl, 2-butenyl, 2-pentenyl, 2-ethyl-3-hexenyl, 3-octenyl, 1-methyl-4-hexenyl, 2-butyl-3-hexenyl.

The term “C₁-C₂₀ alkyl groups optionally containing heteroatoms” means linear or branched alkyl groups having from 1 to 20 carbon atoms, wherein at least one of the hydrogen atoms is substituted by a heteroatom selected from: halogens such as, for example, fluorine, chlorine, bromine, preferably fluorine; nitrogen; sulfur; oxygen. Specific examples of C₁-C₂₀ alkyl groups optionally containing heteroatoms are: fluoromethyl, difluoromethyl, trifluoromethyl, trichloromethyl, 2,2,2-trifluoroethyl, 2,2,2-trichloroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, perfluoropentyl, perfluorooctyl, perfluorodecyl, oxymethyl, thiomethyl, thioethyl.

The term “C₄-C₁₂ cycloalkyl groups” means cycloalkyl groups having from 4 to 12 carbon atoms. Said cycloalkyl groups can be optionally substituted with one or more groups, the same or different from each other, selected from: halogen atoms; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of cycloalkyl groups are: cyclopropyl, 2,2-difluorocyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, methoxycyclohexyl, fluorocyclohexyl, phenylcyclohexyl, decalin, abiethyl.

The term “C₄-C₁₁ heterocyclic groups” means rings having from 4 to 11 atoms, saturated or unsaturated, containing at least one heteroatom selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus, optionally condensed with other aromatic or non-aromatic rings. Said heterocyclic groups can be optionally substituted with one or more groups, the same or different from each other, selected from: halogen atoms, such as, for example, fluorine, bromine, chlorine, preferably fluorine; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of heterocyclic groups are: pyrrolidine, methoxypyrrolidine, piperidine, fluoropiperidine, methylpiperidine, dihydropyridine, piperazine, morpholine, thiazine, induline, phenylindoline, 2-ketoazetidine, diketopiperazine, tetrahydrofuran, tetrahydrothiophene.

The term “C₆-C₂₄ aryl groups” means aromatic carbocyclic groups. Said aryl groups can be optionally substituted with one or more groups, the same or different from each other, selected from: halogen atoms such as, for example, fluorine, chlorine, bromine, preferably fluorine; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of aryl groups are: phenyl, methylphenyl, trimethylphenyl, methoxyphenyl, hydroxyphenyl, phenyloxyphenyl, fluorophenyl, pentafluorophenyl, chlorophenyl, bromophenyl, nitrophenyl, dimethylaminophenyl, naphthyl, phenylnaphthyl, phenanthrene, anthracene.

The term “heteroaryl groups” means aromatic heterocyclic groups, penta- or hexa-atomic, also benzocondensed or heterobicyclic, containing from 1 to 4 heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus. Said heteroaryl groups can be optionally substituted with one or more groups, the same or different from each other, selected from: halogen atoms such as, for example, fluorine, bromine, chlorine, preferably fluorine; hydroxyl groups; C₁-C₁₂ alkyl groups; C₁-C₁₂ alkoxyl groups; cyano groups; amino groups; nitro groups. Specific examples of heteroaryl groups are: pyridine, methylpyridine, methoxypyridine, phenylpyridine, fluoropyridine, pyrimidine, pyridazine, pyrazine, triazine, tetrazine, quinoline, quinoxaline, quinazoline, furan, thiophene, hexylthiophene, bromothiophene, dibromothiophene, pyrrole, oxazole, thiazole, isooxazole, isothiazole, oxadiazole, thiadiazole, pyrazole, imidazole, triazole, tetrazole, indole, benzofuran, benzothiophene, benzooxazole, benzothiazole, benzooxadiazole, benzothiadiazole, benzopyrazole, benzimidazole, benzotriazole, triazolepyridine, triazolepyrimidine, coumarin.

The term “trialkyl- or triaryl-silyl groups” means silane groups containing three C₁-C₁₂ alkyl groups, or three C₆-C₁₂ aryl groups. Specific examples of trialkyl- or triaryl-silyl groups are: trimethyl-silyl, triethyl-silyl, trihexyl-silyl, tridodecyl-silyl, dimethyldodecyl-silyl, triphenyl-silyl, methyldiphenyl-silyl, dimethylnaphthyl-silyl.

The term “alkoxyl or aryloxyl groups” means groups having an oxygen atom attached to a C₁-C₁₂ alkyl group or to a C₆-C₁₂ aryl group. Specific examples of alkoxyl or aryloxyl groups are: methoxyl, ethoxyl, propoxyl, butoxyl, isobutoxyl, 2-ethylhexyloxyl, phenoxyl, benzyloxyl, naphthyloxyl.

The term “thioalkoxyl or thioaryloxyl groups” means groups having an oxygen atom and a sulfur atom attached to a C₁-C₁₂ alkyl group or to a C₆-C₁₂ aryl group. Specific examples of thioalkoxyl or thioaryloxyl groups are: thiomethoxyl, thioethoxyl, thiopropoxyl, thiobutoxyl, thioisobutoxyl, 2-ethylthiohexyloxyl, thiophenoxyl, thiobenzyloxyl.

The term “cyclo” means a system containing a ring containing from 3 to 12 carbon atoms, optionally containing heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus. Specific examples of cyclo are: toluene, benzonitrile, cycloheptatriene, cyclooctadiene, pyridine, thiadiazole, pyrrole, thiophene, selenophene, t-butylpyridine, 1,4-dioxane.

The organic dye having general formula (I) may be prepared by processes known in the art, for example, by the nickel-catalyzed cross-coupling reaction of Grignard reagent of alkyl bromothiophene and α-α′-dibromo-oligothiophenes, such as described, for example, by Kromer J. et al. in the article “Homologous series of regioregular alkylsubstituted oligothiophenes up to an 11-mer”, Tetrahedron (2001), Vol. 57, pg. 3785-3794; or by the Vilsmaier-Heck formilation of thiophene groups, such as described, for example, by Roquet S. et al. in the article “Triphenylamine-Thienylenevinylene Hybrid Systems with Internal Charge Transfer as Donor Materials for Heterojunction Solar Cells”, Journal of American Chemical Society (2006), Vol. 128, No. 10, pg. 3459-3466; or by the reaction of formil derivatives with cyanoacetic acid such as described, for example, by Mikroyannidis J. A. et al. in the article “Triphenylamine- and benzothiadiazole-based dyes with multiple acceptors for application in dye-sensitized solar cells”, Journal of Power Sources (2010), Vol. 195, Issue 9, pg. 3002-3010.

According to a further aspect, the present invention also relates to a dye-sensitized photoelectric transformation element comprising at least one organic dye having general formula (I), said dye-sensitized photoelectric transformation element being supported on oxide semiconductor particles.

The photoelectric transformation element according to the present invention may be prepared by a process for preparing a dye-sensitized photoelectric transformation element for dye-sensitized solar cells (DSSCs) of the prior art, except of using the organic dye having general formula (I).

Preferably, the photoelectric transformation element according to the present invention, is prepared by forming oxide semiconductor thin film on a substrate and subsequently supporting the organic dye having general formula (I) on the thin film.

The substrate on which the oxide semiconductor thin film is formed preferably has a conductive surface, and is commercially available. Preferably, said substrate may be selected, for example, from: glass; transparent polymers such as, for example, polyethyleneterephthalate, polyethersulfone, or mixtures thereof. Preferably, said substrate may have conductivity lower than or equal to 1000Ω, more preferably lower than or equal to 100Ω.

As the oxide semiconductor particles, metal oxide is preferable. Preferably, said oxide semiconductor may be selected, for example, from: titanium dioxide, tin oxide, zinc oxide, tungsten oxide, zirconium oxide, gallium oxide, indium oxide, yttrium oxide, niobium oxide, tantalum oxide, vanadium oxide, or mixtures thereof. More preferably, titanium dioxide, tin oxide, zinc oxide, niobium oxide, indium oxide, or mixtures thereof, may be used, titanium dioxide, zinc oxide or tin oxide, or mixtures thereof, may be even more preferable, and titanium dioxide may be most preferable.

The oxide semiconductor particles may preferably have an average diameter ranging from 1 nm to 500 nm, more preferably ranging from 1 nm to 100 nm, and those having large diameter and those having small diameter may be mixed, or used in multi-layers.

The oxide semiconductor thin film may be prepared by means of different know techniques such as, for example: by spraying oxide semiconductor particles to form a thin film thereof directly on a substrate; by electrically depositing a semiconductor particle thin film using a substrate as an electrode; by applying semiconductor particle slurry or paste containing particles obtained by hydrolysis of suitable precursors such as a metal halogenide or a metal alkoxide, on a substrate (“doctor-blade” technique), and drying, curing or sintering. Preferably, paste may be applied on a substrate, and in this case, slurry may be obtained by dispersing semiconductor oxide particles, with particle diameter ranging from 1 nm to 200 nm, in a dispersion medium by a method known in the art.

As the dispersion medium, those capable of dispersing semiconductor particles may be used without limitation. Preferably, said dispersion medium may be selected, for example, from: water; alcohols such as, for example, ethanol; ketones such as, for example, acetone, acetylacetone; hydrocarbons such as, for example, hexane; or mixtures thereof. Water may be preferable because it minimizes change in viscosity of slurry. Optionally, a dispersion stabilizer may be used in order to stabilize the dispersion of the oxide semiconductor particles. Preferably, said dispersion stabilizer may be selected, for example, from: acids such as, for example, acetic acid, hydrochloric acid, nitric acid, acrylic acid; ketones such as, for example, acetylacetone; glycols such as, for example, polyethyleneglycol; alcohols such as, for example, polyvinylalcohol; or mixtures thereof.

The substrate on which slurry is applied may be sintered, and the sintering temperature may be higher than or equal to 100° C., preferably higher than or equal to 200° C. In any case, the upper limit of the sintering temperature may be the melting point or the softening point of the substrate, commonly 900° C., preferably 600° C. The sintering time may not be specifically limited, but preferably within 4 hours.

The thickness of the thin film on the substrate may ranges from 1 μm to 200 μm, preferably may ranges from 1 μm to 50 μm. The oxide semiconductor thin film may be subjected to a secondary treatment. For example, the thin film may be immersed in a solution of alkoxide, chloride, nitride, or sulfide, of the metal identical to the semiconductor, and dried or re-sintered, thereby improving the property of the thin film. The metal alkoxide may be selected, for example, from: titanium ethoxide, titanium isopropoxide, titanium t-butoxide, n-dibutyl-diacetyl tin, or mixtures thereof. Preferably, an alcohol solution of said metal alkoxide may be used. The metal chloride may be selected, for example, from: titanium tetrachloride, tin tetrachloride, zinc chloride, or mixtures thereof. Preferably, an aqueous solution of said metal chloride may be used. Thus obtained oxide semiconductor thin film may be comprised of oxide semiconductor particles.

The method for supporting organic dye on oxide semiconductor particles in the form of a thin film may not be specifically limited, and for example, a substrate having the oxide semiconductor thin film formed thereon may be immersed in a solution obtained by dissolving the organic dye having general formula (I) in a solvent capable of dissolving the same, or in a dispersion obtained by dispersing said organic dye having general formula (I). The concentration of the solution or of the dispersion, may be appropriately determined. Immersion temperature may range from −60° C. to 100° C., preferably from 0° C. to 50° C., more preferably is room temperature (25° C.), and immersion time may range from about 1 minute to 48 hours, preferably from 1 hour to 26 hours. The solvent used for dissolving the organic dye may be selected, for example, from: methanol, ethanol, acetonitrile, dichloromethane, dimethylsulfoxide, dimethylformamide, acetone, t-butanol, or mixtures thereof. Usually, the concentration of the solution may range from 1×10⁻⁶ M to 1 M, preferably from 1×10⁻⁵ M to 1×10⁻¹ M. Thus, a dye-sensitized photoelectric transformation element comprising oxide semiconductor particles on a dye-sensitized thin film, may be obtained.

Optionally, the organic dye having general formula (I) may be mixed with other organic dyes or metal complex dyes. The metal complex dyes that may be mixed may include, although not specifically limited, ruthenium complex or quaternary salt thereof, phthalocyanin, porphyrin; and the other organic dyes that may be mixed may include metal-free phthalocyanin, porphyrin, cyanin, merocyanin, oxonol, or triphenylmethane dye, methyne dye such as acrylate dyes described in European Patent Application EP 1,311,001, xanthenes, azo, anthraquinone, perylene dye (as described, for example by Nazeeruddin M. K., in Journal of the American Chemical Society (1993), Vol. 115, pag. 6382-6390). In case two or more kinds of organic dyes are used in combination, they may be sequentially absorbed in a semiconductor thin layer, or mixed, dissolved and absorbed.

In order to prevent aggregation of the organic dye on the oxide semiconductor thin layer, optionally, the organic dye having general formula (I), may be mixed with an inclusion compound: the obtained mixture may be adsorbed on a semiconductor thin layer. The inclusion compound may be selected, for example, from: cholic acids such as deoxycholic acid, dehydrodeoxycholic acid, kenodeoxycholic acid, cholic acid methyl ester, cholic acid sodium; polyethyleneoxides; crown ethers; cyclodextrins; calyxarenes; polyethyleneoxides; or mixtures thereof.

After the organic dye is supported, the surface of a semiconductor electrode may be treated with a compound which can be selected from: amine compounds such as, for example, 4-t-butyl pyridine; alcohols such as, for example, methanol, ethanol, butanol, or mixtures thereof; organic acids such as, for example, acetic acid, propionic acid, or mixtures thereof; or mixtures thereof. For example, a substrate having a dye-supported semiconductor particle thin film formed thereon may be immersed in an ethanol solution of amine.

According to a further aspect, the present invention also relates to a dye-sensitized solar cell (DSSC) comprising the dye-sensitized photoelectric transformation element above described.

Said dye-sensitized solar cell (DSSC) may be prepared by methods know in the art of preparing a dye-sensitized solar cell (DSSC) using photoelectric transformation element of the prior art, except of using a dye-sensitized photoelectric transformation element comprising oxide semiconductor particles where the organic dye having general formula (I) is supported. The dye-sensitized solar cell (DSSC) may comprise a photoelectric transformation element electrode (negative electrode) wherein the organic dye having general formula (I) is supported on the oxide semiconductor particles, a counter electrode (positive electrode), redox electrolyte, hole-transport material, or p-type semiconductor.

Preferably, the dye-sensitized solar cell (DSSC) according to the present invention may be prepared by coating titanium dioxide paste on a transparent conductive substrate; sintering the coated substrate to form a titanium dioxide thin film; immersing the substrate having titanium dioxide thin film formed thereon in a mixed solution in which the organic dye having general formula (I) is dissolved, so as to form a dye-absorbed titanium dioxide film electrode; providing a second transparent conductive substrate having a counter electrode formed thereon; forming a hole penetrating the second transparent conductive substrate and the counter electrode; placing thermoplastic polymer film between the counter electrode and the dye-absorbed titanium dioxide film electrode and heat-pressing them to join the counter electrode and the titanium dioxide film electrode; injecting electrolyte into the thermoplastic polymer film placed between the counter electrode and the titanium dioxide film electrode through the hole; and, sealing the hole with suitable materials which may be selected, for example, from thermoplastic polymers.

The redox electrolyte, hole-transport material, or p-type semiconductor may be liquid, a coagulated form (gel and gel phase), solid. The liquid may be selected, for example, from those obtained by dissolving redox electrolyte, dissolved salt, hole-transport material, or p-type semiconductor in a solvent, and a room temperature dissolved salt. The coagulated form (gel and gel phase) may be selected, for example, from those obtained by including redox electrolyte, a dissolved salt, hole-transport material, or p-type semiconductor in a polymer matrix or low molecular gellant. The solid may be selected, for example, from redox electrolyte, a dissolved salt, hole-transport material, or p-type semiconductor.

The hole-transport material may be selected, for example, from: amine derivatives; conductive polymers such as, for example, polyacetylene, polyaniline, polythiophene; or discotic liquids crystal phase such as, for example, triphenylene. The p-type semiconductor may be selected, for example, from CuI, CuSCN. As the counter electrode, those having conductivity and catalytic function on reduction of redox electrolyte may be preferably used, and, for example, those obtained by depositing platinum, carbon, rhodium, ruthenium, on a glass or a polymer film, or applying conductive particles thereon may be used.

The redox electrolyte used in the dye-sensitized solar cell (DSSC) according to the present invention may include halogen redox electrolyte comprising halogen compounds comprising halogen ion as a counter ion and a halogen molecule; metal redox electrolytes such as ferrocyanide-ferrocyanide or ferrocene-ferricynium ion; metal complexes such as cobalt complexes; organic redox electrolytes such as, for example, alkylthio-alkyldisulfide, viologen dye, hydroquinone-quinone; halogen redox electrolytes may be preferable. As the halogen molecule comprised in the halogen redox electrolyte, an iodine molecule may be preferable. As the halogen compounds comprising halogen ion as counter ion, a halogenated metal salt such as, for example, LiI, NaI, KI, CaI₂, MgI₂, CuI, or an organic ammonium salt of halogen such as, for example, tetraalkylammonium iodide, imidazolium iodide, pyridium iodide, or I₂ may be used.

In case the redox electrolyte is in the form of a solution comprising the same, an electrochemically inert solvent may be used. For example, acetonitrile, propylenecarbonate, etylenecarbonate, 3-methoxypropionitrile, methoxy-acetonitrile, valeronitrile, ethyleneglycol, propyleneglycol, diethyleneglycol, triethyleneglycol, butyrolactone, dimethoxyethane, dimethylcarbonate, 1,3-dioxolane, methylformate, 2-methyltetrahydrofurane, 3-methoxy-oxazolidin-2-on, sulforane, tetrahydrofurane, water, may be used. Acetonitrile, valeronitrile, propylenecarbonate, ethylenecarbonate, 3-methoxypropionitrile, ethyleneglycol, 3-methoxy-oxazolidin-2-on, or butyrolactone, may be preferable. Said solvents may be used alone or in combination.

As a gel phase positive electrolyte, those obtained by including electrolyte or electrolyte solution in oligomer or polymer matrix, or including electrolyte or electrolyte solution in a starch gellant, may be used.

The concentration of the redox electrolyte may preferably ranges from 0.01% by weight to 99% by weight, and more preferably from 0.1% by weight to 30% by weight, with respect to the total weight of the solution.

The dye-sensitized solar cell (DSSC) according to the present invention may be obtained by disposing a photoelectric transformation element (negative electrode) wherein the organic dye is supported on oxide semiconductor particles on a substrate and a counter electrode (positive electrode) opposite thereto, and filling a redox electrolyte containing solution therebetween.

The present invention will be further illustrated below by means of the following examples which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLES Reagents and Materials

The reagents and materials used in the following examples, as well as their manufacturers, have been below reported:

-   -   N-bromosuccinimmide (Aldrich): used as such;     -   2-bromo-3-octyl-thiophene (Aldrich): used as such;     -   dimethylformamide (DMF) (Aldrich): used as such or optionally         anhydrified on magnesium (Mg);     -   diethyl ether (Aldrich): used as such;     -   sodium bicarbonate (NaHCO₃) (Aldrich): used as such or in a 1 M         aqueous solution;     -   sodium sulfate (Aldrich): used as such;     -   petroleum ether (Aldrich): used as such;     -   dibromoethane (Aldrich): used as such;     -   anhydrous diethyl ether (Aldrich): used as such;     -   magnesium turnings (Aldrich): used as such;     -   2,5-dibromothiophene (Aldrich): used as such;     -   1,3-bis(diphenylphosphino)propane]dichloronickel(II)         [Ni(dppp)Cl₂]: (Aldrich): used as such;     -   hydrochloric acid (HCl) solution 2 M (Aldrich): used as such or         diluted with water;     -   magnesium sulfate (Aldrich): used as such;     -   chloroform (Aldrich): used as such;     -   acetic acid (Aldrich): used as such;     -   dichloromethane (CH₂Cl₂) (Aldrich): used as such;     -   1,2-dichloroethane (Aldrich): used as such;     -   tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄](Aldrich):         used as such;     -   anhydrous toluene (Aldrich): used as such;     -   phosphorous oxychloride (Aldrich): used as such;     -   sodium acetate (C₂H₃NaO₂) (Aldrich): used as such;     -   cyanoacetic acid (Aldrich): used as such;     -   ammonium acetate (Aldrich): used as such;     -   glacial acetic acid (Aldrich): used as such;     -   sodium hydroxide (NaOH) (Aldrich): used as such;     -   ethanol (Carlo Erba): used as such;     -   n-butyl lithium (2.5 M in hexane) (Aldrich): used as such;     -   anhydrous tetrahydrofuran (THF) (Aldrich): used as such;     -   hexane (Carlo Erba): used as such;     -   Celite® 545 (Aldrich): used as such;     -   tributyltin chloride (Aldrich): used as such;     -   2-(3-thienyl)benzoic acid (Aldrich): used as such;     -   bromine (Br₂) (Aldrich): used as such;     -   aluminum trichloride (AlCl₃) (Aldrich): used as such;     -   carbon disulfide (CS₂) (Aldrich): used as such;     -   3-(3-thienyl)acrylic acid (Aldrich): used as such;     -   palladium on activated charcoal (Pd—C) (10% by weight of Pd)         (Aldrich): used as such;     -   ammonium formate (Aldrich): used as such;     -   iso-propanol (iPrOH) (Carlo Erba): used as such;     -   thionyl chloride (SOCl₂) (Aldrich): used as such;     -   3,4-ethylenedioxythiophene (Aldrich): used as such;     -   titanium tetrachloride (Aldrich): used as such;     -   N-methyl-N-butylimidazolium iodide (Aldrich): used as such;     -   iodine (Carlo Erba): used as such;     -   lithium iodide (Aldrich): used as such;     -   guanidinium-thiocyanate (Aldrich): used as such;     -   t-butylpyridine (Aldrich): used as such;     -   valeronitrile (Aldrich): used as such;     -   acetonitrile (Carlo Erba): used as such;     -   2,5-bis(tributylstannyl)thiophene (Aldrich): used as such;     -   5-bromo-2-thiophenecarbaldheyde (Aldrich): used as such;     -   sodium fluoride (Aldrich) used as such.

In the following examples the characterization methods below reported have been used.

NMR Spectra

The NMR spectra of the obtained compounds have been carried out with a spectrometer NMR Bruker Avance 400.

To this aim, about 10 mg of the sample to be examined have been dissolved in about 0.8 ml of a suitable deuterated solvent directly on the glass pipe used for the measurement. The chemical shifts scale has been calibrated with respect to the tetramethylsilane signal set to 0 ppm.

Mass Spectra

The mass spectra of the compounds obtained have been carried out with a reverse-geometry double-focusing spectrometer AT 95S DCI (“Desorption Chemical Ionization”) with iso-butane as reagent gas in ions positive mode. The filament emission current has been calibrated at 0.1 mA with an electron beam energy equal to 100 eV and with a ions source temperature kept to 90° C.

Example 1 Synthesis of 5-carboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ia)

Synthesis of 2-(3-octylthienyl)magnesium bromide having formula (2)

In a 100 ml flask, a solution of 2-bromo-3-octylthiophene having formula (1) (3.0 g, 10.89 mmol) and dibromoethane (0.93 ml, 10.89 mmol) in 10 ml of anhydrous diethyl ether, was added, dropwise to a suspension of magnesium turnings (Mg) (0.53 g) in 50 ml of anhydrous diethyl ether, under argon (Ar) atmosphere, sonicated for 30 minutes, and heated at the reflux temperature of the solvent for another 90 minutes: after the elimination of the excess of magnesium turnings by filtration, a solution containing 2-(3-octylthienyl)magnesium bromide having formula (2) (Grignard reagent) was obtained and was immediately used in the following coupling reaction.

Synthesis of 3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (3)

A solution of 2-(3-octylthienyl) magnesium bromide having formula (2), obtained as described above, was slowly added, at 0° C., in a 100 ml flask containing a solution of 2,5-dibromothiophene (0.4 ml, 3.63 mmol) and 1,3-bis(diphenylphosphino)propane]dichloronickel(II) [Ni(dppp)Cl₂](181 mg, 0.4 mmol) in 50 ml of anhydrous diethyl ether. The obtained reaction mixture was heated at the reflux temperature of the solvent, for 18 hours, subsequently cooled to room temperature (25° C.) and then treated with a mixture of crushed ice and 50 ml of hydrochloric acid (HCl) solution (2 M). Subsequently, the cooled reaction mixture was extracted with diethyl ether (3×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was thoroughly washed with water, 1 M aqueous solution of sodium bicarbonate (NaHCO₃), brine, again with water, and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using petroleum ether as eluent obtaining 1.65 g (97% yield) of 3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (3), as a yellow liquid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.18 (d, 2H), 7.05 (s, 2H), 6.94 (d, 2H), 2.77 (t, 4H), 1.65-1.59 (m, 4H), 1.39-1.26 (m, 20H), 0.87 (t, 6H).

Synthesis of 5-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (4)

In a 100 ml flask, N-bromosuccinimide (NBS) (0.3 g, 1.75 mmol) was added, in small portions, to a solution of 3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (3) (1.24 g, 2.62 mmol), obtained as described above, in 50 ml of a mixture of chloroform and acetic acid (1:1), at 0° C. The obtained reaction mixture was heated at room temperature (25° C.) and stirred for additional 3 hours. Subsequently, the reaction mixture was poured into water and extracted with dichloromethane (CH₂Cl₂) (3×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was thoroughly washed with water, 1 M aqueous solution of sodium bicarbonate (NaHCO₃), brine, again with water, and then was dried over sodium sulfate (Na₂SO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using petroleum ether as eluent obtaining 0.60 g (63% yield) of 5-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (4), as a slightly yellow oil, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.19 (d, 1H), 7.04 (d, 1H), 6.99 (d, 1H), 6.94 (d, 1H), 6.89 (s, 1H), 2.78-2.68 (m, 4H), 1.68-1.58 (m, 4H), 1.35-1.24 (m, 20H), 0.89-0.84 (m, 6H).

Synthesis of 3,3″,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″: 5′″″-2″″″-heptathiophene having formula (5)

In a 200 ml flask, a mixture of 5-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (4) (0.5 g, 0.9 mmol), obtained as described above, 2,5-bis(tributylstannyl)thiophene (0.27 g, 0.41 mmol) and tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄](100 mg, 0.085 mmol) in 100 ml of anhydrous toluene, was heated at the reflux temperature of the solvent overnight. Subsequently, the reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 30 ml of dichloromethane (CH₂Cl₂) and the obtained solution was washed with 1 M aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), subsequently with water (3×20 ml), and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane (CH₂Cl₂) and petroleum ether (1:3) as eluent obtaining 0.42 g (47% yield) of 3,3′,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (5), as a reddish oil, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.19 (d, 2H), 7.08-7.04 (m, 6H) 7.01 (s, 2H), 6.95 (d, 2H), 2.81-2.74 (m, 8H), 1.73-1.60 (m, 8H), 1.39-1.23 (m, 40), 0.90-0.82 (m, 12H).

Synthesis of 5-formyl-3,3″,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:5′″,5″″:-2″″:2′″″:5′″″,2″″″-heptathiophene having formula (6)

In a 100 ml flask, a Vilsmeier reagent, which was prepared with phosphorous oxychloride (POCl₃) (0.05 ml, 0.49 mmol) in dry dimethylformamide (DMF) (0.04 ml, 0.49 mmol), was added to a cold solution (0° C.) of 3,3″,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:-5′″″,2″″″-heptathiophene having formula (5) (0.36 g, 0.35 mmol), obtained as described above, in 20 ml of 1,2-dichloroethane under argon (Ar) atmosphere. After being stirred, at 70° C., for 20 hours, the obtained reaction mixture was cooled to room temperature (25° C.), diluted with dichloromethane (CH₂Cl₂), treated with a solution of sodium acetate (C₂H₃NaO₂), then stirred at room temperature (25° C.), for 2 hours, and subsequently extracted with dichloromethane (CH₂Cl₂) (3×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was washed with 1 M aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), subsequently with water, and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane (CH₂Cl₂) and petroleum ether (1:1) as eluent obtaining 0.12 g (34% yield) of 5-formyl-3,3″,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (6), as a reddish solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 9.83 (s, 1H), 7.59 (s, 1H), 7.25 (d, 1H), 7.19 (d, 1H), 7.12 (d, 1H), 7.08-7.05 (m, 3H), 7.02-7.01 (m, 2H), 6.95 (d, 1H), 2.85-2.74 (m, 8H), 1.70-1.58 (m, 8H), 1.40-1.21 (m, 40), 0.90-0.85 (m, 12H).

Said compound having formula (6) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 182.4, 141.1, 141.0, 140.3, 140.1, 139.7, 139.0, 138.0, 136.2, 135.5, 135.4, 134.5, 134.4, 130.2, 130.1, 129.7, 128.8, 127.8, 126.6, 126.0, 125.9, 124.4, 124.2, 123.8, 31.8, 30.7, 30.5, 30.4, 30.3, 29.5, 29.4, 29.2, 22.6, 14.1.

Furthermore, said compound having formula (6) was also characterized by mass spectra: HRMS (ESI) obtaining: [M]: 1052.4258 (0.4 ppm), calculated for C₆₁H₈₀OS₇: 1052.4254.

Synthesis 5-carboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-2,2′:5′,2″:5″,2′″:5′″,5″″:-2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ia)

In a 100 ml flask, 5-formyl-3,3″,3″″,3″″″-tetraoctyl-2,2′:5′,2″:5″,2′″:-5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (6) (100 mg, 0.09 mmol), obtained as described above, was mixed with cyanoacetic acid (NC—CH₂—COOH) (40 mg, 0.19 mmol) and with a solution of ammonium acetate (CH₃COO⁻NH₄ ⁺) (80 mg, 0.47 mmol) in 40 ml of glacial acetic acid (CH₃COOH): the obtained solution was heated at the reflux temperature of the solvent, for 12 hours. The obtained reaction mixture was slowly cooled to room temperature (25° C.), obtaining a dark precipitate which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 5-carboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ia) (70 mg, 66% yield), as a black solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 10.85 (s, 1H), 8.30 (s, 1H) 7.77 (s, 1H), 7.14 (d, 1H), 7.30 (d, 1H), 7.25 (d, 1H), 7.21-7.19 (m, 3H), 7.17 (s, 1H), 7.15 (d, 1H), 7.11 (d, 1H) 6.98 (d, 1H), 2.84-2.74 (m, 8H), 1.7-1.60 (m, 8H), 1.14-1.12 (m, 40), 0.90-0.85 (m, 12H).

Said compound having formula (Ia) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 163.8, 145.9, 141.6, 141.1, 140.8, 140.3, 139.3, 139.2, 139.0, 136.6, 134.6, 134.2, 134.0, 133.2, 130.8, 130.6, 129.7, 129.0, 126.8, 126.6, 126.4, 126.3, 124.7, 116.3, 110.1, 109.5, 99.7, 32.6, 31.4, 31.2, 30.9, 30.3, 30.2, 30.0, 29.8, 23.3, 14.2.

Furthermore, said compound having formula (Ia) was also characterized by mass spectra: HRMS (ESI) obtaining: [M]: 1119.4323 (1.1 ppm) calculated for C₆₄H₈₁NO₂S₇: 1119.4312.

Example 2 Synthesis of 5-carboxycyanovinylen-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (Ib)

Synthesis of 5-tributylstannyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene (7)

In a 100 ml flask n-butyl lithium (LiBu) (0.51 ml, 2.5 M in hexane, 1.27 mmol) was added dropwise, at 0° C., to a solution containing the compound having formula (3) (0.5 g, 1.06 mmol), obtained as described in Example 1, dissolved in 40 ml of dry tetrahydrofurane (THF), under argon (Ar) atmosphere. The obtained reaction mixture was stirred for 30 minutes, at 0° C. Subsequently, tributyltin chloride (SnBu₃Cl) (0.33 ml, 1.16 mmol) was added, dropwise, at 0° C. and the obtained reaction mixture was allowed to warm slowly to room temperature (25° C.). After dilution with diethyl ether (30 ml), a saturated aqueous solution of sodium fluoride (NaF) was added and the obtained reaction mixture was stirred, for 1 hour, at room temperature (25° C.). The obtained precipitate was filtered off by using Celite® 545 and the obtained filtrate was washed with a saturated aqueous solution of sodium bicarbonate (NaHCO₃), subsequently with water and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure obtaining 5-tributylstannyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (7) which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.16 (d, 1H), 7.04 (s, 2H), 6.95 (s, 1H), 6.95 (d, 1H), 2.77 (t, 4H), 1.67-1.54 (m, 10H), 1.39-1.26 (m, 26H), 1.13-1.08 (m, 6H), 0.94-0.84 (m, 15H).

Synthesis of 5-formyl-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (8)

In 50 ml flask a mixture of 5-bromo-2-thiophenecarbaldehyde (0.03 ml, 0.26 mmol), 5-tributylstannyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (7) (0.24 g, 0.31 mmol), obtained as described above, and tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄](61 mg, 0.052 mmol) in 20 ml of anhydrous toluene was heated at the reflux temperature of the solvent for 20 hours. The obtained reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 30 ml of dichloromethane (CH₂Cl₂) and the organic phase was washed with a 1 M aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), subsequently with water (3×20 ml) and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane and petroleum ether (1/1) as eluent obtaining 0.25 g (92% yield) of 5-formyl-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (8), as a yellowish solid, which was characterized by ¹H NMR (400 MHz, CDCl₃) obtaining the following spectrum: 9.85 (s, 1H), 7.67 (d, 1H), 7.23 (d, 1H), 7.21 (d, 1H), 7.20 (s, 1H), 7.12 (d, 1H), 7.08 (d, 1H), 6.95 (d, 1H), 2.78 (t, 4H), 1.70-1.61 (m, 4H), 1.39-1.26 (m, 20H), 0.87 (t, 6H).

Said compound having formula (8) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 182.3, 146.8, 141.4, 140.6, 139.9, 137.3, 136.9, 134.8, 133.3, 132.6; 130.1, 130.0, 129.0, 126.4, 126.0, 123.9, 31.8, 30.6, 30.4, 29.5, 29.4, 29.3, 29.2, 22.6, 14.0.

Furthermore, said compound having formula (8) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 582.2 and 582.2133 (2.5 ppm), respectively, calculated for C₃₃H₄₂OS₄: 582.2119.

Synthesis of 5-carboxycyanovinylen-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (Ib)

In a 250 ml flask were introduced 0.19 g (2.47 mmol) of 5-formyl-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (8), obtained as described above, and mixed with cyanoacetic acid (NC—CH₂—COOH) (71 mg, 0.82 mmol), ammonium acetate (CH₃COO⁻NH₄ ⁺) (0.19 g, 2.47 mmol) and 100 ml of glacial acetic acid (CH₃COOH). The solution was heated at the reflux temperature of the solvent, for 12 hours. After slowly cooling the reaction mixture to room temperature (25° C.), a dark precipitate was formed, which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 140 mg (53% yield) of 5-carboxycyanovinylen-4′,3′″-dioctyl-2,2′:5′,2″:5″,2′″-quaterthiophene having formula (Ib), as a black solid, which was characterized by ¹H NMR (400 MHz, CDCl₃) obtaining the following spectrum: 8.28 (s, 2H), 7.68 (d, 1H), 7.23 (d, 1H), 7.20 (d, 1H), 7.12 (d, 1H), 7.07 (d, 1H), 6.95 (d, 1H), 2.78 (t, 4H), 1.68-1.60 (m, 4H), 1.40-1.27 (m, 20H), 0.87 (t, 6H).

Said compound having formula (Ib) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 167.9, 148.8, 147.6, 141.0, 140.6, 140.0, 137.2, 134.7, 133.8, 133.7, 132.7, 130.2, 130.0, 126.6, 126.1, 124.2, 124.0, 115.6, 95.6, 31.8, 30.6, 30.4, 29.6, 29.5, 29.4, 29.3, 29.2, 22.6, 14.1.

Furthermore, said compound having formula (8) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 649.3 and 649.2159 (2 ppm), respectively, calculated for C₃₆H₄₃NO₂S₄: 649.2177.

Example 3 Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-carboxycyanovinylene having formula (Ic)

Synthesis of 8H-indeno[2,1-b]thiophen-8-one having formula (11)

In a 50 ml flask, a mixture of 2-(3-thienyl)benzoic acid having formula (9) (2.14 g, 10.49 mmol) and thionyl chloride (SOCl₂) (3.7 ml, 50.35 mmol) was stirred overnight, at 45° C., under argon (Ar) atmosphere. Subsequently, after the evaporation of the excess of thionyl chloride (SOCl₂), the obtained 2-(3-thienyl)benzoyl chloride having formula (10), as a brown oil, was immediately used in the following reaction. Under argon (Ar) atmosphere, a solution of 2-(3-thienyl)benzoyl chloride having formula (10) in carbon disulfide (CS₂) (30 ml) was added dropwise, over a period of 5 minutes, through a dropping funnel, to a 250 ml three-necked round bottom flask containing a suspension of aluminium trichloride (AlCl₃) (3.26 g, 24.13 mmol) in carbon disulfide (CS₂) (40 ml), under stirring. The obtained reaction mixture was heated at the reflux temperature of the solvent, for 6 hours, subsequently cooled to room temperature (25° C.) and then treated with a mixture of crushed ice and 50 ml of hydrochloric acid (HCl) solution (2 M). Subsequently, the cooled reaction mixture was extracted with diethyl ether (2×40 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was washed with a saturated aqueous solution of sodium chloride (NaCl) (3×20 ml) and then dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using dichloromethane (CH₂Cl₂) as eluent obtaining 1.47 g (76% yield) of 8H-indeno[2,1-b]thiophen-8-one having formula (11), as yellow solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.74 (d, 1H), 7.47 (d, 1H), 7.33 (m, 1H); 7.17 (d, 1H), 7.16 (m, 1H), 7.12 (d, 1H).

Synthesis of 2-bromo-8H-indeno[2,1-b]thiophen-8-one having formula (13)

In a 100 ml flask, bromine (Br₂) (0.54 ml, 10.54 mmol) was added, dropwise, to a solution of 8H-indeno[2,1-b]thiophen-8-one having formula (11) (1.40 g, 7.53 mmol), obtained as described above, in 30 ml of chloroform, at 0° C. The obtained reaction mixture was heated at room temperature (25° C.) and stirred for additional 7 hours. Subsequently, the reaction mixture was poured into water and extracted with dichloromethane (CH₂Cl₂) (3×30 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was thoroughly washed with water, aqueous solution of sodium bicarbonate (NaHCO₃), brine, again with water, and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of petroleum ether and dichloromethane (CH₂Cl₂) (1:1) as eluent obtaining 1.78 g (90% yield) of 2-bromo-8H-indeno[2,1-b]thiophen-8-one having formula (13), as a yellow-orange powder, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.47 (ddd, 1H), 7.34 (td, 1H), 7.19 (td, 1H), 7.17 (s, 1H); 7.13 (ddd, 1H).

Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-one having formula (14)

In a 100 ml flask, a mixture of 2-bromo-8H-indeno[2, 1-b]thiophen-8-one having formula (13) (0.21 g, 0.78 mmol), obtained as described above, 5-tributylstannyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (7) (0.71 g, 0.94 mmol), obtained as described in Example 2, and tetrakis(triphenylphosphine) palladium(0) [Pd(PPh₃)₄](91 mg, 0.077 mmol) in 50 ml of anhydrous toluene, was heated at the reflux temperature of the solvent for 20 hours. Subsequently, the reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 30 ml of dichloromethane (CH₂Cl₂) and the obtained solution was washed with 1 M aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), subsequently with water (2×20 ml), and then was dried over magnesium sulphate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of petroleum ether and dichloromethane (CH₂Cl₂) (1:2) as eluent obtaining 0.30 g (60% yield) 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-one having formula (14), as a dark orange solid, which was characterized by ¹H NMR (500 MHz, CDCl₃) obtaining the following spectrum: 7.48 (d, 1H), 7.36 (ddd, 1H), 7.21-7.16 (m, 5H), 7.13 (d, 1H), 7.08 (d, 1H), 6.96 (d, 1H), 2.78 (t, 4H), 1.74-1.61 (m, 4H), 1.40-1.27 (m, 20H), 0.87 (t, 6H).

Said compound having formula (14) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 185.2, 159.1, 151.5, 140.7, 140.0, 139.2, 137.8, 136.9, 134.8, 133.9, 133.6, 133.4, 132.4, 130.1, 130.0, 128.5, 128.4, 126.4, 126.1, 124.0, 123.7, 119.5, 115.8, 31.8, 30.7, 30.5, 29.5, 29.4, 29.3, 29.2, 22.6, 14.0.

Furthermore, said compound having formula (14) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 656.4 and 656.2275 (<1 ppm), respectively, calculated for C₃₉H₄₄OS₄: 656.2275

Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-carboxycyanovinylene having formula (Ic)

In a 250 ml flask, 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-one having formula (14) (0.27 g, 0.41 mmol), obtained as described above, was mixed with cyanoacetic acid (NC—CH₂—COOH) (71 mg, 0.82 mmol) and with a solution of ammonium acetate (CH₃COO⁻NH₄ ⁺) (0.16 g, 2.46 mmol) in 80 ml glacial acetic acid (CH₃COOH): the obtained solution was heated at the reflux temperature of the solvent, for 72 hours. The obtained reaction mixture was slowly cooled to room temperature (25° C.), obtaining a dark precipitate which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 0.15 g, (50% yield) of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-8H-indeno[2,1-b]thiophen-8-carboxycyanovinylene having formula (Ic), as a black solid, which was characterized by ¹H NMR (300 MHz, THF-d₈) obtaining the following spectrum: 8.50 (d, 1H), 7.47-7.41 (m, 3H), 7.36 (ddd, 1H) 7.32 (d, 1H), 7.24 (ddd, 1H), 7.20 (d, 1H), 7.13 (d, 1H), 6.99 (d, 1H), 2.86-2.79 (m, 4H), 1.50-1.62 (m, 4H), 1.39-1.29 (m, 20H), 0.88 (t, 6H).

Said compound having formula (Ic) was also characterized by ¹³C NMR (75 MHz, THF-d₈) obtaining the following spectrum: 155.1, 152.5, 152.3, 141.5, 140.5, 140.4, 138.7, 137.6, 135.7, 135.3, 134.7, 132.6, 132.5, 130.7, 130.6, 129.1, 128.2, 127.2, 126.9, 126.8, 125.0, 120.7, 117.3, 116.1, 32.7, 31.4, 31.2, 30.3, 30.2, 30.1, 30.0, 29.9, 23.3, 14.2.

Furthermore, said compound having formula (Ic) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 723.8 and 723.2333 (<1 ppm), respectively, calculated for C₄₂H₄₅NO₂S₄: 723.2333.

Example 4 Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]-thiophen-6(5H)-carboxycyanovinylene having formula (Id)

Synthesis of 3-(3-thienyl)propionic acid having formula (16)

In a 100 ml flask, 1.52 g of palladium on activated charcoal (Pd—C) (10% by weight of Pd) and ammonium formate (3.23 g, 51.22 mmol), were added to a solution of 3-(3-thienyl)acrylic acid having formula (15) (2.6 g, 17 mmol) in 40 ml of iso-propanol (iPrOH): the obtained reaction mixture was heated at the reflux temperature of the solvent, for 6 hours. Subsequently, the reaction mixture was cooled to room temperature (25° C.), filtered through Celite® 545 and subsequently evaporated under reduced pressure. The obtained residue was dissolved in 50 ml of dichloromethane (CH₂Cl₂) and the obtained solution was treated with 20 ml of a hydrochloric acid (HCl) solution (0.1 M). The obtained organic phase was washed with water (3×10 ml) and subsequently evaporated at reduced pressure obtaining 2.3 g (90% yield) of 3-(3-thienyl)propionic acid having formula (16), as a colorless solid, which was characterized by 1H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.28 (dd, 1H), 7.01-6.99 (m, 1H), 6.96 (d, 1H), 2.89 (t, 2H), 2.69 (t, 2H).

Synthesis of 3-(2,5-dibromothiophen-3-yl)propionic acid having formula (17)

In a 100 ml flask, a solution of bromine (Br₂) (1.28 ml, 0.02 mol) in 30 ml of chloroform was added to a solution of 3-(3-thienyl)propionic acid having formula (16) 1.9 g (12.16 mol), obtained as disclosed above, in 30 ml of chloroform, at 0° C. The obtained reaction mixture was heated at room temperature (25° C.), stirred for additional 2 hours and subsequently poured into ice. Subsequently, the cooled reaction mixture was extracted with diethyl ether (2×40 ml). The overall organic phase (obtained by joining the organic phases obtained as described above, was washed with a saturated aqueous solution of sodium chloride (NaCl) (3×20 ml) and then dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure obtaining, after crystallization from hexane, 2.41 g (64% yield) of 3-(2,5-dibromothiophen-3-yl)propionic acid having formula (17), as a colorless solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 6.82 (s, 1H), 2.86 (t, 2H), 2.63 (t, 2H).

Synthesis of 2-bromo-4,5-dihydroeyclopenta[b]thiophen-6-one having formula (18)

In a 50 ml flask, 3-(2,5-dibromothiophen-3-yl)propionic acid having formula (17) (0.65 g, 2.07 mmol), obtained as described above, was treated with 0.75 ml of thionyl chloride (SOCl₂) and the obtained reaction mixture was heated at the reflux temperature of the solvent, for 5 minutes. Subsequently, the reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained yellow oil was dissolved in 15 ml of dichloromethane (CH₂Cl₂): subsequently, aluminum trichloride (AlCl₃) (0.82 g, 6.21 mmol) was added and the obtained reaction mixture was heated at the reflux temperature of the solvent, for 10 minutes. Subsequently, the obtained reaction mixture was cooled to room temperature (25° C.) and then treated with a mixture of crushed ice and 20 ml of hydrochloric acid (HCl) solution (0.1 M). Subsequently, the cooled reaction mixture was extracted with chloroform (2×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was washed with a diluted aqueous solution of sodium hydroxide (NaOH), with a hydrochloric acid (HCl) solution (0.1 M) (2×20 ml), then with water (4×20 ml) and subsequently dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using dichloromethane (CH₂Cl₂) as eluent obtaining 0.13 g (32% yield) of 2-bromo-4,5-dihydroeyclopenta[b]thiophen-6-one having formula (18), as a colorless powder, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 7.09 (s, 1H), 3.03-3.00 (m, 2H), 2.91-2.87 (m, 2H).

Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]-thiophen-6(5H)-one having formula (19)

In a 100 ml flask, a mixture of 2-bromo-4,5-dihydroeyclopenta[b]thiophen-6-one having formula (18) (0.12 g, 0.53 mmol), obtained as described above, 5-tributylstannyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (7) (0.40 g, 0.53 mmol), obtained as described in Example 2, and tetrakis(triphenylphosphine) palladium(0) [Pd(PPh₃)₄](0.062 g, 0.053 mmol) in 30 ml of anhydrous toluene, was heated at the reflux temperature of the solvent, for 20 hours. Subsequently, the obtained reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 40 ml of dichloromethane (CH₂Cl₂) and the obtained solution was washed with a 1 M aqueous solution of sodium bicarbonate (NaHCO₃) (2×10 ml), then with water (3×20 ml) and subsequently dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane (CH₂Cl₂) and petroleum ether (2:1) as eluent obtaining 0.20 g (63% yield) of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]thiophen-6(5H)-one having formula (19), as an orange solid, which was characterized by ¹H NMR (500 MHz, CDCl₃) obtaining the following spectrum: 7.20 (d, 1H), 7.16 (s, 1H), 7.11 (d, 1H), 7.08 (d, 1H), 6.95 (d, 2H), 3.03-3.00 (m, 2H), 2.96-2.93 (m, 2H), 2.78 (t, 4H), 1.70-1.59 (m, 4H), 1.39-1.26 (m, 20H), 0.87 (t, 6H).

Said compound having formula (19) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 196.7, 169.2, 152.2, 140.7, 140.0, 138.4, 136.9, 134.9, 133.8, 132.5, 130.1, 130.0, 128.7, 126.4, 126.1, 124.0, 119.4, 40.5, 31.8, 30.7, 30.5, 29.5, 29.4, 29.3, 29.2, 24.1, 22.6, 14.0.

Furthermore, said compound having formula (19) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 608.3 and 608.2277 (3.2 ppm), respectively, calculated for C₃₅H₄₄OS₄: 608.2275.

Synthesis of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]-thiophen-6(5H)-carboxycyanovinylene having formula (Id)

In a 100 ml flask, 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]thiophen-6(5H)-one having formula (19) (0.18 g, 0.29 mmol), obtained as described above, was mixed with cyanoacetic acid (NC—CH₂—COOH) (0.051 g, 0.59 mmol) and with a solution of ammonium acetate (CH₃COO⁻NH₄ ⁺) (0.14 g, 1.78 mmol) in 80 ml of glacial acetic acid (CH₃COOH): the obtained solution was heated at the reflux temperature of the solvent, for 72 hours. The obtained reaction mixture was slowly cooled to room temperature (25° C.), obtaining a dark precipitate which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 0.035 g (17% yield) of 2-(3,3″-dioctyl-[2,2′:5′,2″-terthiophen]-5-yl)-4H-cyclopenta[b]thiophen-6(5H)-carboxy-cyanovinylene having formula (Id), as a black solid, which was characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M-CO₂]: 631.5 and 631.2444 (1 ppm), respectively, calculated for [C₃₈H₄₅NO₂S₄—CO₂]: 631.2435.

Example 5 Synthesis of 5-carboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ie)

Synthesis of 5-formyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (20)

In a 100 ml flask, a Vilsmeier reagent, which was prepared with phosphorous oxychloride (POCl₃) (0.5 ml, 5.3 mmol) in dry dimethylformamide (DMF) (3 ml), was added to a cold solution (0° C.) of 3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (3) (0.36 g, 0.35 mmol), obtained as described in Example 1, in 50 ml of 1,2-dichloroethane, under argon (Ar) atmosphere. After being stirred, at 70° C., for 24 hours, the obtained reaction mixture was cooled to room temperature (25° C.), diluted with dichloromethane (CH₂Cl₂), treated with a solution of sodium acetate (C₂H₃NaO₂), then stirred at room temperature (25° C.), for 2 hours, and subsequently extracted with dichloromethane (CH₂Cl₂) (3×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was washed with water (2×20 ml), subsequently with brine (2×10 ml), and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane (CH₂Cl₂) and petroleum ether (1:1) as eluent obtaining 1.58 g (89% yield) of 5-formyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (20) which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 9.83 (s, 1H), 7.59 (s, 1H), 7.27 (dd, 2H), 7.10 (d, 1H), 6.96 (d, 1H), 2.85-2.75 (m, 4H), 1.17-1.54 (m, 4H), 1.14-1.26 (m, 20H), 0.88-0.85 (m, 6H).

Synthesis of 5-formyl-5″-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (21)

In a 250 ml flask, N-bromosuccinimide (NBS) (0.61 g, 3.44 mmol) was added, in small portions, to a solution of 5-formyl-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (20) (1.57 g, 3.13 mmol), obtained as described above, in 100 ml of a mixture of chloroform and acetic acid (1:1), at 0° C. The reaction mixture was heated at room temperature (25° C.) and stirred for additional 3 hours. Subsequently, the obtained reaction mixture was poured into water and extracted with dichloromethane (CH₂Cl₂) (4×20 ml). The overall organic phase (obtained by joining the organic phases obtained as described above) was thoroughly washed with water, 1 M aqueous solution of sodium bicarbonate (NaHCO₃), brine, again with water, and then was dried over sodium sulfate (Na₂SO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using petroleum ether as eluent obtaining 1.6 g (89% yield) 5-formyl-5″-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (21), as a slightly yellow oil, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 9.83 (s, 1H), 7.59 (s, 1H), 7.23 (d, 1H), 7.05 (d, 1H), 6.91 (s, 1H), 2.81 (t, 2H), 2.71 (t, 2H), 1.73-1.56 (m, 4H), 1.14-1.26 (m, 20H), 0.89-0.85 (m, 6H).

Synthesis of 2,5-bis(tributylstannyl)-3,4-ethylenedioxythiophene having formula (23)

In a 100 ml flask n-butyl lithium (LiBu) (5.8 ml, 2.5 M in hexane, 14.8 mmol) was added dropwise, at −20° C., to a solution containing 3,4-ethylenedioxythiophene having formula (22) (1 g, 7.04 mmol) dissolved in 30 ml of dry tetrahydrofurane (THF), under argon (Ar) atmosphere. The obtained reaction mixture was stirred for 1 hour, at −20° C. Subsequently, tributyltin chloride (SnBu₃Cl) (4.2 ml, 14.8 mmol) was added, dropwise, and the reaction mixture was maintained, under stirring, at −20° C., for 30 minutes: then, the reaction mixture was allowed to warm slowly to room temperature (25° C.). After dilution with diethyl ether (30 ml), a saturated aqueous solution of sodium fluoride (NaF) was added and the reaction mixture was stirred, for 1 hour, at room temperature (25° C.). The obtained precipitate was filtered off by using Celite® 545 and the obtained filtrate was washed with a saturated aqueous solution of sodium bicarbonate (NaHCO₃), subsequently with water and then was dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure obtaining 2,5-bis(tributylstannyl)-3,4-ethylenedioxythiophene having formula (23) which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 4.11 (s, 4H), 1.64-1.44 (m, 12H), 1.38-1.26 (m, 12H), 1.12-1.05 (m, 12H), 0.94-0.86 (m, 18H).

Synthesis of 5-formyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (24)

In a 100 ml flask, a mixture of 5-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (4) (0.4 g, 0.8 mmol), obtained as described in Example 1, 5-formyl-5″-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (21) (0.5 g, 0.8 mmol), obtained as described above, 2,5-bis(tributylstannyl)-3,4-ethylenedioxythiophene having formula (23) (0.49 g, 0.68 mmol), obtained as described above, and tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄](0.10 g, 0.085 mmol) in 50 ml of anhydrous toluene, was heated at the reflux temperature of the solvent, for 12 hours. Subsequently, the obtained reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 50 ml of dichloromethane (CH₂Cl₂) and the obtained solution was washed with a saturated aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), then with water (3×10 ml) and subsequently dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using a mixture of dichloromethane (CH₂Cl₂) and petroleum ether (1:1) as eluent obtaining 0.19 g (20% yield) of 5-formyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (24), as a reddish solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 9.83 (s, 1H), 7.59 (s, 1H), 7.24-7.20 (m, 2H), 7.18 (d, 1H), 7.12-7.04 (m, 4H), 6.96-6.93 (m, 1H), 4.42 (s, 4H), 2.86-2.75 (m, 8H), 1.73-1.60 (m, 8H), 1.14-1.12 (m, 40), 0.90-0.85 (m, 12H).

Said compound having formula (24) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 182.6, 141.2, 140.4, 140.1, 139.7, 139.6, 137.9, 137.6, 135.8, 134.1, 132.9, 132.0, 130.3, 130.0, 129.3, 128.3, 127.8, 126.0, 125.9, 125.7, 123.7, 109.8, 109.2, 65.0, 64.9, 31.8, 30.7, 30.5, 30.3, 29.7, 29.6, 29.5, 29.4, 29.2, 22.6, 14.1.

Furthermore, said compound having formula (24) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 1110.4 and 1110.4408 (0.1 ppm), respectively, calculated for C₆₃H₈₂O₃S₇: 1110.4309.

Synthesis of 5-carboxycyanovynilen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ie)

In a 100 ml flask, 5-formyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (24) (0.13 g, 0.12 mmol), obtained as described above, was mixed with cyanoacetic acid (NC—CH₂—COOH) (0.02 g, 0.23 mmol) and with a solution of ammonium acetate (CH₃COO⁻NH₄ ⁺) (0.05 g, 0.58 mmol) in 40 ml glacial acetic acid (CH₃COOH): the obtained solution was heated at the reflux temperature of the solvent, for 12 hours. The obtained reaction mixture was slowly cooled to room temperature (25° C.), obtaining a dark precipitate which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 0.10 g (73% yield) of 5-carboxycyanovynilen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (Ie), as a black solid, which was characterized by ¹H NMR (300 MHz, THF-d₈) obtaining the following spectrum: 8.22 (s, 1H) 7.62 (s, 1H), 7.33 (d, 1H), 7.18 (d, 2H), 7.14 (d, 1H), 7.08-7.04 (m, 4H), 6.94 (d, 1H), 4.43 (s, 4H), 2.84-2.74 (m, 8H), 1.7-1.60 (m, 8H), 1.14-1.12 (m, 40), 0.90-0.85 (m, 12H).

Said compound having formula (Ie) was also characterized by ¹³C NMR (75 MHz, THF-d₈) obtaining the following spectrum: 163.8, 145.9, 141.6, 141.1, 140.8, 140.3, 139.3, 139.2, 139.0, 136.6, 134.6, 134.2, 134.0, 133.2, 130.8, 130.6, 129.7, 129.0, 126.8, 126.6, 126.4, 126.3, 124.7, 116.3, 110.1, 109.5, 99.7, 32.6, 31.4, 31.2, 30.9, 30.3, 30.2, 30.0, 29.8, 23.3, 14.2.

Furthermore, said compound having formula (Ie) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 1177.4 and 1177.4358 (0.1 ppm), respectively, calculated for C₆₆H₈₃NO₄S₇: 1177.4367.

Example 6 Synthesis of 5,5″″″-dicarboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (If)

Synthesis of 5,5″″″-diformyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (25)

In a 50 ml flask, a mixture of 2,5-bis(tributylstannyl)-3,4-ethylenedioxythiophene having formula (23) (0.28 g, 0.39 mmol), obtained as described in Example 5, 5-formyl-5″-bromo-3,3″-dioctyl-2,2′:5′,2″-terthiophene having formula (21) (0.50 g, 0.86 mmol), obtained as described in Example 5, and tetrakis(triphenylphosphine)palladium(0) [Pd(PPh₃)₄](0.10 g, 0.085 mmol) in 20 ml of anhydrous toluene, was heated at the reflux temperature of the solvent for 12 h. Subsequently, the obtained reaction mixture was cooled to room temperature (25° C.) and the solvent was evaporated at reduced pressure. The obtained residue was dissolved in 30 ml of dichloromethane (CH₂Cl₂) and the obtained solution was washed with a saturated aqueous solution of sodium bicarbonate (NaHCO₃) (2×20 ml), then with water (4×10 ml) and subsequently dried over magnesium sulfate (MgSO₄), at room temperature (25° C.), for 3 hours. The solvent was subsequently evaporated at reduced pressure and the obtained residue was purified by chromatography on silica gel using dichloromethane (CH₂Cl₂) as eluent obtaining 0.11 g (44% yield) of 5,5″″″-diformyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (25), as a reddish solid, which was characterized by ¹H NMR (300 MHz, CDCl₃) obtaining the following spectrum: 9.83 (s, 2H), 7.59 (s, 2H), 7.53 (d, 2H), 7.15-7.05 (m, 4H), 4.42 (s, 4H), 2.86-2.75 (m, 8H), 1.73-1.60 (m, 8H), 1.14-1.12 (m, 40), 0.90-0.85 (m, 12H).

Said compound having formula (25) was also characterized by ¹³C NMR (75 MHz, CDCl₃) obtaining the following spectrum: 182.5, 141.2, 140.5, 140.2, 140.1, 139.1, 138.4, 137.9, 134.2, 132.8, 128.5, 127.9, 126.0, 125.8, 109.6, 65.0, 31.9, 31.8, 30.5, 30.3, 29.6, 29.5, 29.4, 29.3, 29.2, 22.6, 14.1.

Furthermore, said compound having formula (25) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 1138.3 and 1110.4254 (0.1 ppm), respectively, calculated for C₆₄H₈₂O₄S₇: 1138.4258.

Synthesis of 5,5″″″-dicarboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (If)

In a 100 ml flask, 5,5″″″-diformyl-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (25) (0.11 g, 0.96 mmol), obtained as described above, was mixed with cyanoacetic acid (NC—CH₂—COOH) (0.033 g, 0.38 mmol) and with a solution of ammonium acetate (CH₃COO⁻NH₄ ⁺) (0.062 g, 0.77 mmol) in 30 ml glacial acetic acid (CH₃COOH): the obtained solution was heated at the reflux temperature of the solvent, for 12 hours. The obtained reaction mixture was slowly cooled to room temperature (25° C.), obtaining a dark precipitate which was recovered by filtration and washed with a diluted aqueous solution of sodium hydroxide and then with water obtaining 0.10 g (82% yield) of 5,5″″″-dicarboxycyanovinylen-[3,3″,3″″,3″″″-tetraoctyl]-3′″,4′″-ethylenedioxy-2,2′:5′,2″:5″,2′″:5′″,5″″:2″″,2′″″:5′″″,2″″″-heptathiophene having formula (If), as a black solid, which was characterized by ¹H NMR (300 MHz, THF-d₈) obtaining the following spectrum: 8.29 (s, 2H), 7.76 (s, 2H), 7.40 (d, 2H), 7.22 (d, 2H), 7.15 (s, 2H), 4.44 (s, 4H), 2.92-2.81 (m, 8H), 1.72 region (8H are under the THF signal), 1.46-1.30 (m, 40), 0.91-0.86 (m, 12H).

Said compound having formula (If) was also characterized by mass spectra: MS MALDI and HRMS (ESI) obtaining: [M]: 1272.4 and 1272.43998 (2 ppm), respectively, calculated for C₇₀H₈₄N₂O₆S₇: 1272.4374.

Example 7 Preparation of Dye-Sensitized Solar Cell (DSSC)

Titanium dioxide (TiO₂) electrodes were prepared by spreading (“doctor-blade” technique) a colloidal paste containing a 20 nm sized titanium dioxide (TiO₂) particles (TiO₂ Paste DSL 18NR-T—Dyesol) on a conductive FTO glass (Hartford Glass Co., TEC 8, having a thickness of 2.3 mm and a sheet resistance of 6 Ω/cm²-9 Ω/cm²), previously cleaned with water and ethanol, immersed in a freshly prepared aqueous titanium tetrachloride (TiCl₄) solution (4.5×10⁻² M), at 70° C., for 30 minutes, and finally washed with ethanol.

After a first drying at 125° C., for 15 minutes, a reflecting scattering layer containing >100 nm sized titanium dioxide (TiO₂) particles (Ti-Nanoxide R/SP—Solaronix) was spread (“doctor-blade” technique) over the first titanium dioxide (TiO₂) layer and sintered till 500° C., for 30 minutes. The titanium dioxide (TiO₂) film-coated glass was cooled to room temperature (25° C.) and immersed again in a freshly prepared aqueous titanium tetrachloride (TiCl₄) solution (4.5×10⁻² M), at 70° C., for 30 minutes, finally washed with ethanol and sintered at 500° C., for 30 minutes, obtaining a final thickness of the electrode of 12 μm.

After sintering, the titanium dioxide (TiO₂) film-coated glass was cooled at about 80° C.-100° C. and immediately immersed into a dichloromethane (CH₂Cl₂) solution (5×10⁻⁴ M] of the compound having formula (Ia), obtained as described in Example 1, at room temperature (25° C.), for 24 h. The dyed titania-glass was washed with ethanol and dried at room temperature (25° C.), under a nitrogen (N₂) flux.

A 50 μm thick Surlyn spacer (TPS 065093-50—Dyesol) was used to seal the photoanode obtained as described above and the counter electrode constituted of a platinized FTO glass (Hartford Glass Co., TEC 8, having a thickness of 2.3 mm and a sheet resistance of 6 Ω/cm²-9 Ω/cm²), subsequently the cell was filled up with the electrolyte solution having the following composition: N-methyl-N-butylimidazolium iodide (0.6 M), iodine (0.04 M), lithium iodide (LiI) (0.025 M), guanidinium-thiocyanate (0.05 M) and t-butylpyridine (0.28 M), in a 15:85 (v/v) mixture of valeronitrile and acetonitrile.

The active area of the cell, calculated by means of a microphotography, was 0.1168 cm².

The photovoltaic performance of the cell was measured with a solar simulator (Abet 2000) equipped with a 300 W Xenon light source, the light intensity was adjusted with a standard calibrated Si solar cell (“VLSI Standard” SRC-1000-RTD-KGS), the current-voltage characteristics were acquired by applying an external voltage to the cell and measuring the generated photocurrent with a “Keithley 2602A” (3 A DC, 10 A Pulse) digital source meter. The following results were obtained:

Voc (open circuit photovoltage)=685 mV;

FF (fill factor)=65.5%;

Jsc (short-circuit photocurrent density)=21.67 mA/cm²;

η (photoelectric transformation efficiency)=9.72%.

Example 8 Preparation of Dye-Sensitized Solar Cell (DSSC)

With the same procedure described in Example 3, a dye-sensitized solar cell (DSSC) was prepared by using an organic dye of formula (Ib) obtained as described in Example 2, and employing an electrolyte solution having the following composition: N-methyl-N-butylimidazolium iodide (0.6 M), iodine (0.04 M), lithium iodide (LiI) (0.025 M), guanidinium-thiocyanate (0.05 M) and t-butylpyridine (0.28 M), in a 15:85 (v/v) mixture of valeronitrile and acetonitrile. In this case the active area of the cell, calculated by means of a microphotography, was 0.0949 cm². The photovoltaic performance of the cell was measured as described in Example 3. The following results were obtained:

Voc (open circuit photovoltage)=663 mV;

FF (fill factor)=68.8%;

Jsc (short-circuit photocurrent density)=16.89 mA/cm²;

η (photoelectric transformation efficiency)=7.71%. 

The invention claimed is:
 1. An organic dye having a formula (I):

wherein: X is a hydrogen atom, or a carboxycyanovinylene group having the formula (II):

wherein R₅ is an hydrogen atom; Z is a carboxycyanovinylene group having the formula (II) or (IV):

wherein R₅ is an hydrogen atom; R₁ and R₂, identical to each other, are a n-hexyl group, a n-octyl group, a n-decyl group, or a n-dodecyl group; R₃ and R₄, identical to or different from each other, are a hydrogen atom or a n-hexyl group, a n-octyl group, a n-decyl group, or a n-dodecyl group; or, R₃ and R₄ are bound to each other to form, together with the other atoms to which they are bound, a saturated cycle containing four carbon atoms and two oxygen atoms; n is 1; p is 0 or 1; and m is
 1. 2. A dye-sensitized photoelectric transformation element comprising the organic dye of claim 1, wherein the dye-sensitized photoelectric transformation element is supported on oxide semiconductor particles.
 3. A dye-sensitized solar cell comprising the dye-sensitized photoelectric transformation element of claim
 2. 4. The organic dye of claim 1, wherein R₁ and R₂ are an n-octyl group.
 5. The organic dye of claim 1, wherein R₃ and R₄, identical or different from each other, are a hydrogen or an n-octyl group.
 6. The organic dye of claim 1, wherein R₃ and R₄ are bound to each other to form a 1,4 dioxane.
 7. A dye-sensitized photoelectric transformation element comprising the organic dye of claim 4, wherein the dye-sensitized photoelectric transformation element is supported on oxide semiconductor particles.
 8. A dye-sensitized photoelectric transformation element comprising the organic dye of claim 5, wherein the dye-sensitized photoelectric transformation element is supported on oxide semiconductor particles.
 9. A dye-sensitized photoelectric transformation element comprising the organic dye of claim 6, wherein the dye-sensitized photoelectric transformation element is supported on oxide semiconductor particles.
 10. A dye-sensitized solar cell comprising the dye-sensitized photoelectric transformation element of claim
 7. 11. A dye-sensitized solar cell comprising the dye-sensitized photoelectric transformation element of claim
 8. 12. A dye-sensitized solar cell comprising the dye-sensitized photoelectric transformation element of claim
 9. 